1 Copyright © 2009 by ASME 

Proceedings of the ASME 2009 Rail Transportation Division Fall Conference 

RTDF2009 

October 20-21, 2009, Ft. Worth, Texas, USA 

RTDF2009-18017 

DETAILED IMPACT ANALYSES FOR DEVELOPMENT OF THE 

NEXT GENERATION RAIL TANK CAR 

Part 2 –Development of Advanced Tank Car Protection Concepts 

Steven W. Kirkpatrick 

Applied Research Associates, Inc. 

Mountain View, CA, USA

ABSTRACT 

Significant research has been conducted over the past few 

years to develop improved railroad tank cars that maintain tank 

integrity for more severe accident conditions than current 

equipment. The approach taken in performing this research is 

to define critical collision conditions, evaluate the behavior of 

current design equipment in these scenarios, and develop 

alternative strategies for increasing the puncture resistance. 

The evaluations are being performed with finite element 

models of the tank cars incorporating a high level of detail. 

Both laboratory scale and full-scale impact tests were 

performed to validate the modeling and ultimately compare the 

effectiveness of current and alternative equipment designs. 

This paper describes the use of the detailed finite element 

impact and puncture analyses to assess the performance of 

advanced puncture protection concepts. 

INTRODUCTION 

Over the last few years, there has been significant attention 

on the potential for release of hazardous materials from railroad 

tank cars. This attention is primarily a result of a series of three 

accidents or derailments between 2002 and 2005 involving the 

release of hazardous material [1-3]. In response, a research 

program was initiated to develop strategies for improving 

railroad tank cars so they can maintain tank integrity for more 

severe accident conditions than current equipment. The 

research was initiated by The Dow Chemical Company (Dow), 

Union Pacific Railroad, and Union Tank Car Company, 

working under Memoranda of Cooperation (MOC) with the 

Federal Railroad Administration, and Transport Canada, and 

separately with the U.S. Transportation Security 

Administration. 

The Next Generation Rail Tank Car (NGRTC) Project was 

organized to include a Core Team (consisting of representatives 

from the signatories to the Memorandum of Cooperation) and a 

group of Lead Contractors. The Core Team and Lead 

Contractors worked together to: 1) evaluate and select 

candidate materials, components, subsystems and systems with 

the potential to provide large performance improvements in the 

safety and security of rail tank cars; 2) select conceptual tank 

car designs incorporating appropriate materials, components 

and systems for improved safety and security; and 3) develop 

and use appropriate models, analytical techniques and testing 

protocols to demonstrate the efficacy of the tank car concepts. 

The goal of the NGRTC program was to develop a conceptual 

tank car that had a five to ten times improvement in the impact 

energy required to puncture the tank car. 

A key effort in this program is the development and 

application of detailed finite element models of tank car 

equipment which can accurately predict the puncture resistance 

under different impact conditions. These analysis tools were 

developed and validated for the puncture of the baseline tank 

cars for both side and head impact conditions [4, 5]. 

This paper describes the results of the NGRTC efforts to 

develop advanced strategies for improving railroad tank cars so 

they can maintain tank integrity for more severe accident 

conditions than current equipment. 

ANALYSES OF ADVANCED PROTECTION SYSTEMS 

The first task in this research was to develop and validate a 

modeling capability that can be used to analyze the impact 

response of a tank car. The results of the model development 

and validation effort are provided in a companion paper [4] and 

in the NGRTC analysis final report [5]. 
 2 Copyright © 2009 by ASME 

The validated puncture modeling capabilities were 

subsequently applied to analyze a series of advanced tank car 

protective structure concepts. Included in these were multilayered foam systems, engineered metal structures (EMS) 

systems, and advanced material (composites) options. 

For some of these concepts, additional material 

characterization testing was required. For example, detailed 

characterization testing was performed on the crushable energy 

absorbing foams [6-8]. The tests were then used to develop 

suitable constitutive models for the various strength foams [5]. 

Example head impact puncture analyses on both a layered 

foam system and a corrugated EMS system are shown in Figure 

1. A variety of designs were investigated using the detailed 

analyses capabilities. In addition, a full scale head test was also 

performed for both of the concepts shown in Figure 1 [9]. 

However, neither of the foam or EMS systems was optimized. 

(a) Layered foam protection system 

(b) Corrugated EMS protection system 

Figure 1. Analyses of advanced protection concepts. 

The failure mode of the layered foam and EMS systems 

was similar to that of the baseline tank systems when impacted 

by the 6x6 inch impactor. When the load acting on a layer of 

the advanced protective system exceeded the shear capacity of 

the layer, the layer would be punctured. For many of the 

advanced concepts, the system design would increase the 

stiffness of the support for the outer layers. The increased 

support structure stiffness would result in outer layer 

penetration at reduced ram displacements. As a result, the 

protection system and commodity tank would be penetrated 

independently at lower peak forces and lower puncture energies 

than could be obtained in an optimized system. 

An example of this failure mode is seen in the impact 

response of an egg-crate core sandwich EMS structure shown 

in Figure 2. The outer EMS sandwich structure consists of a 

core that is a rectangular grid of axial and radial webs with a 4 

inch spacing and face sheets that are fully bonded to the core. 

The face sheets are made of 8 gauge (0.1644”) steel and the 

core webs are made of 5 gauge (0.2092”) steel. 

(a) Calculated impact response 

(b) Calculated impact response 

Figure 2. Calculated side impact response and penetration for a 

4-inch egg crate EMS system. 
 3 Copyright © 2009 by ASME 

The intermediate stage of deformation for the egg-crate 

EMS is shown in Figure 3. At this point in the response the 

outer face sheet has already been punctured and the core under 

the penetrator face is being crushed. These sandwich structures 

are very efficient for developing stiffness and strength for 

distributed loading conditions or under uniform crushing. 

However, the high stiffness of the system subjected to the 

localized punch load results in a penetration at relatively low 

levels of displacement. Thus, under these localized loading 

conditions the EMS structure absorbs very little impact energy 

for the total amount of weight required for the protective 

sandwich structure. 

Figure 3. Calculated intermediate impact damage for a 4-inch 

egg crate EMS system. 

A variety of different approaches were evaluated to 

improve the puncture protection capabilities of the foam and 

EMS systems. The performance of advanced protective 

systems was typically improved when the thickness of the outer 

layer was increased to resist puncture and the stiffness of the 

supporting structure was reduced to increase the displacements 

of the system before the puncture level was exceeded. These 

effects are seen by considering the three protections concepts 

shown in Figure 4. The concepts include two different 

corrugated EMS designs and a single monolithic plate, all of 

which have approximately equivalent weight. The different 

corrugated EMS designs illustrate the approach of moving 

weight from the inner face sheet and core structure to lower the 

system stiffness and increasing the outer face sheet thickness to 

improve the penetration resistance. The maximum 

extrapolation of this concept is to move all of the EMS weight 

into a single thicker outer jacket. 

The calculated puncture behavior of the three protection 

options are compared in Figure 5. The ram punctures the 

baseline 6-inch corrugated EMS structure at a load of 

approximately 200,000 lbs and a ram displacement of 

approximately 6 inches. Thus, the energy dissipation of this 

EMS structure is quite small. The ram punctures the modified 

3-inch corrugated EMS structure at a load of approximately 

600,000 lbs and a ram displacement of approximately 12 

inches. Thus, the energy dissipation of this EMS structure is 

approximately 5 times that of the original 6-inch EMS concept. 

Alternatively, the 0.5625-inch-thick jacket is not penetrated 

until a force of approximately 1.1 million lbs and an impactor 

displacement of approximately 30 inches. Thus, the jacket 

absorbs significantly more impact energy than either of the 

corrugated EMS structures for the 6-inch impactor. 

Figure 4. Alternative EMS tank protection concepts. 

The calculated forces to puncture the outer layer of the 

foam and EMS systems are added to the plot of the puncture 

force versus system thickness in Figure 6. The difference in 

the data for the advanced systems is that the thickness used is 

the layer thickness only (e.g. outer head shield or outer face 

sheet thickness) rather than the sum of the total tank and jacket 

layer thicknesses. The comparison shows that the foam and 

EMS structures had the effect of making each layer act 

independently rather than coming in contact and working 

together to resist the high shear stresses around the edge of the 

impactor. With this effect the impactor is able to puncture each 

layer of the system sequentially without fully engaging the 

other layers in the system. As a result, the maximum 

achievable puncture forces were reduced and the systems that 

were analyzed did not reach the desired puncture energies. 
 4 Copyright © 2009 by ASME 

Figure 5. Comparison of the force-deflection behaviors for the 

Corrugated EMS concepts. 

Although the systems with a monolithic jacket performed 

better than the corrugated EMS structures in this example, the 

conclusion can not be generalized to all EMS designs and 

impact scenarios. The EMS structures would be expected to 

perform significantly better under a more distributed loading. 

Other benefits of the EMS concepts are that the structural 

stiffness can be used to efficiently carry the train service loads 

in a “tank within a tank” design. Further analysis of other EMS 

concepts (e.g. core geometries, materials) and more general 

impact conditions would be required to obtain an optimized 

design. 

Figure 6. EMS puncture forces as a function of outer layer 

thickness. 

A similar set of observations was obtained from the 

analysis of layered foam systems. In general, the systems 

analyzed did not outperform a single monolithic plate of 

equivalent protection system weight for the 6x6 inch impactor. 

However, the performance for larger impactors and the 

optimum foam and interface properties to maximize 

performance were not fully explored. In addition, low density 

foams can contribute to improved thermal insulation. If a foam 

system can maintain a lower average shipping temperature (and 

thus a lower average tank pressure), the overall tank puncture 

energy could potentially be increased. 

Composite Material Protection Systems 

The above analyses indicate that a tank protection system 

developed using only traditional tank car designs will have 

difficulty reaching the five to ten times protection goal of the 

NGRTC program. To achieve a five times increase in the 

puncture energy of tank cars while maintaining a comparable 

level of utility will require new design approaches and 

advanced materials. The candidate materials for advanced 

protection concepts include polymeric composite materials. 

Tank car concepts with composite protection systems were 

not evaluated as thoroughly as the layered foam and EMS 

concepts and no testing of composite systems was performed in 

the NGRTC program. However, some preliminary evaluations 

were performed to assess the potential of composites for 

puncture resistance. 

A brief literature search was performed to identify 

candidate composite systems that can be used for tank car 

impact protection and data that can be used to assess the 

potential protection levels. One of the promising material 

systems is an S-2 glass fiber composite for which a range of 

punch tests had been previously performed and reported in 

open literature sources [10-15]. This material has been used in 

applications requiring penetration resistance and the published 

information included results from various punch test 

configurations. In addition, a detailed composite damage 

model for this material system had been developed and 

implemented in LS-DYNA [16, 17]. Published material 

parameters were available and the model had been validated 

against the punch test results. 

A summary of the normalized peak punch test loads for the 

S-2 Glass composite system and various candidate tank car 

steels are plotted against aerial density is shown in Figure 7. 

The normalized punch loads are the shear stress around the 

punch perimeter scaled by the material density since many tank 

car designs are operationally constrained by the amount of 

additional weight that can be added to the protection system. 

As a result, the punch shear resistance is compared on an 

equivalent weight basis rather than an equivalent thickness 

basis. The data in the figure were taken from the punch tests 

performed on steels in the NGRTC program [18-20] and 

composite punch tests reported in open literature sources for a 

woven S-2 glass fiber SC-15 polymeric matrix composite 

system. 

The comparisons in Figure 7 are not perfect due to some 

differences in the punch test protocols between steels and 

composites. For example, the punch used in the composite 

tests had a sharp edge around the face and the NGRTC punch 

had a radius applied around the perimeter of the punch face. 

However, the comparison indicates that there is potential for 
 5 Copyright © 2009 by ASME 

puncture resistance improvements using composite materials. 

At the largest aerial density testing for the composite, a direct 

comparison can be made with 11 gauge A1011 steel and the 

HSLA 90XF. The composite out performs A1011 by 

approximately 70% and HSLA 90x by roughly 10%. Further 

improvements in the performance of the composite system 

could likely be obtained by optimizing the composite material 

and/or layup for these types of impact conditions. 

Figure 7. Normalized peak punch test loads versus aerial 

density for various materials. 

Some preliminary tank car impact analyses were 

performed with LS-DYNA to assess the potential puncture 

protection of the composite material. The first step in this 

process was to validate the implementation of the composite 

damage model in the current version of LS-DYNA being used 

for the puncture analyses. Models of the punch tests were 

developed to validate the *MAT_COMPOSITE_MSC_DMG 

material model in LS-DYNA. Our approach was to model the 

same experiments performed by Xiao et al [12] and confirm the 

agreement between simulations and experiments reported. The 

LS-DYNA models of the punch simulations were developed 

based on descriptions provided by Xiao et al in Reference 12. 

When the simulations of the punch test were repeated in 

this study, the agreement of the model with the punch tests was 

not obtained. An example of the performance is shown in 

Figure 8. The agreement is good in the initial loading of the 

specimen and the onset of damage. However, in all of the cases 

analyzed, the model predicts a premature failure and the full 

puncture force and punch displacement prior to failure was not 

achieved. 

A likely reason for the lack of agreement between 

simulations and tests was the functionality of the material 

model in different versions of LS-DYNA. Significant effort 

was expended in working with LSTC and MSC to have a 

version of LS-DYNA functioning correctly with material 162. 

Material 162 is formally supported by MSC, but LSTC 

provides versions of LS-DYNA with this material model. A 

request was made to MSC for LS-DYNA models that could be 

used to validate that the material model was functioning 

correctly in the versions of LS-DYNA built for ARA. MSC 

provided single element models to proof various functions of 

the model. However, these single element tests do not provide a 

comprehensive way of assessing the models functionality as 

there is damage growth that occurs based on the state of 

surrounding elements. Several requests were made to MSC for 

additional models to test the functionality of material 162. 

Unfortunately, none were provided that could be validated 

against other results. 

Figure 8. Comparison of punch test data and simulations. 

Given these limitations in the composite damage model, it 

was still desirable to perform an analysis of a composite tank 

car system. A model was developed to assess the puncture 

resistance of the 500 lb chlorine tank car with a composite 

jacket retrofit. A 1.5-inch thick composite jacket was placed 

around the commodity tank. A composite with this thickness 

has approximately the same weight as a steel jacket with a 

thickness of 0.355 inches (that the same tank car retrofit with a 

0.375-inch steel jacket was previously analyzed in the NGRTC 

Program [5]). A (0/90) layup with principal material directions 

coincident with the hoop and axial tank directions and equal 

numbers of 0 degree and 90 degree layers was used. The 

model for the commodity tank is the same as discussed in the 

previous analyses. 

The model developed for the composite jacket is similar to 

the approach used for steel materials. Inside the impact zone, a 

very fine mesh of solid elements was used where the detailed 

damage and failure behavior can be assessed. Outside the 

impact zone, the jacket was modeled with shell elements. 

These were connected to solid elements in the impact zone, 

much like the approach used for modeling the commodity tank. 

To reduce the model size, this region was modeled with 12 

thick plies of the composite fabric. In reality, a composite this 

thick would require approximately 64 plies of fabric where 

delamination could occur between each layer. To model each 

ply, a minimum of 64 elements would be needed through the 
 6 Copyright © 2009 by ASME 

thickness. Instead, the composite was modeled with 12 layers 

with 3 elements through the thickness of each ply, resulting in 

36 elements through the thickness. Elements therefore have a 

characteristic length of about .042 inches (1 mm). 

Delamination can still occur in the model, but only between 

each of the 12 layers. 

Preliminary analyses with the composite jacket and tank 

model are shown in Figure 9. The time shown corresponds to a 

ram displacement of 18 inches and the current impact load is in 

excess of 500,000 lbs. The composite jacket has significant 

damage and has failed around much of the perimeter of the 

contact patch. Based on the observed level of damage, it is not 

expected that the calculation would predict puncture forces that 

are significantly greater than that of an equivalent weight steel 

jacket. However, the composite model is also expected to 

under predict the composite strength in this analysis. 

(a) Calculated impact response 

(b) Detail of the puncture behavior 

Figure 9. Punch-shear mode in composite jacket at 18 inches 

of displacement. 

One effect seen in the analyses is the potential for the 

composite to provide a blunting of the impact loads on the 

commodity tank. A comparison of the impact behavior of a 

1.5-inch thick composite jacket with an equivalent weight steel 

jacket is shown in Figure 10. The comparison clearly shows a 

blunting of the loads on the commodity tank for the same level 

of impact displacement and this effect has potential for 

delaying the development of damage and penetration of the 

tank. The magnitude of this blunting effect would be expected 

to increase as the thickness of the composite jacket becomes 

greater. 

(a) 1.5 inch composite jacket 

(b) 0.375 inch A1011 steel jacket 

Figure 10. Composite jacket blunting effect for a tank side 

impact. 

Impact Performance Summary 

A summary of the current state of tank car side impact 

performance is provided in Figure 11. From the full scale side 

impact Test 2, the 105J500W tank car puncture energy was 

slightly less than one million ft-lbs. This corresponds to a 10 
 7 Copyright © 2009 by ASME 

mph impact with a 286,000 lb ram car and the 6x6 inch 

impactor. From analyses, the puncture energies of the 

105J300W and 105J600W tank cars are approximately 30 

percent less and 40 percent greater than the 105J500W tank car, 

respectively. 

The goal of the Next Generation Railroad Tank Car Project 

was to increase the puncture energy of the tank car by five to 

ten times over the baseline 105J500W tank car design. This 

target is outlined by the red box in Figure 11. The proposed 

toxic inhalation hazard (TIH) tank car standard [21] fell within 

this range (25 mph impact), requiring a puncture energy that is 

6 times that of the baseline tank car. However, the levels that 

were found to be achievable with the first generation concepts 

in the NGRTC project are more consistent with two to three 

times the puncture energy of the baseline design. 

Figure 11. Summary of side impact puncture performance and 

goals. 

A similar summary of the current state of tank car head 

impact performance is provided in Figure 12. The calculated 

puncture energy for a pressurized (100 psi) 105J500W tank 

head with an 11-gauge head jacket is 610,000 ft-lbs [4, 5]. This 

corresponds to an 8 mph impact with the 286,000 lb ram car 

and the 6x6 inch impactor. For comparison, the puncture 

energy of a 105J600W tank head with a 0.50 inch full height 

head shield is 1.1 million ft-lbs. 

The goal of the Next Generation Railroad Tank Car Project 

was to increase the puncture energy of the tank car by five to 

ten times over the baseline 105J500W tank head as outlined by 

the red box in Figure 12. The proposed TIH tank car standard 

is above this range, requiring a puncture energy that is 

approximately 14 times that of the baseline tank head (30 mph 

impact). However, the levels that were found to be achievable 

with the first generation concepts in the NGRTC project are 

more consistent with 2.5 to 4 times the puncture energy of the 

baseline design. 

ACKNOWLEDGMENTS 

This report is based on work funded by The Dow Chemical 

Company, on behalf of the Next Generation Rail Tank Car 

(NGRTC) Project. The development of the puncture modeling 

methodologies and the testing used to validate the models and 

develop the constitutive and failure models were all performed 

under the NGRTC project. 

Figure 12. Summary of head impact puncture performance and 

goals. 

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